Recently, high-luminance light emitting elements, such as light emitting diodes (hereinafter, occasionally abbreviated to LEDs), have been developed for each of RGB that stands for red, green, and blue known as primary colors of light, and the production of large-scale self-luminance full color displays is being started. Among others, LED displays have characteristics that they can be lightweight and slimmed-down, and that they consume less power, etc. Hence, a demand for the LED displays as large-scale displays that can be used outdoors has been sharply increasing. Also, the use of the LED displays has been diversified, and there has been a need for a system flexibly adaptable to various applications, such as large-scale TV sets, advertisements, billboards, traffic information, stereoscopic displays, and illuminations.
Generally, the dynamic driving method is used as a driving method of the LED display. To be more specific, in the case of an LED display composed of a dot matrix with m row and n columns (m and n are integers equal to 2 or greater), the anode terminals of the LEDs positioned on each row are commonly connected to one common line, and the cathode terminals of the LEDs positioned on each column are commonly connected to one current supply line. As many common lines as m rows are switched ON successively at a predetermined cycle, and an LED driving current is supplied to as many current supply lines as n columns according to image data corresponding to the switched-ON line. Consequently, the LED driving current according to the corresponding image data is applied to the LED in each pixel, whereby an image is displayed.
In the case of a large-scale LED display set outdoors, a plurality of LED units are combined to form the LED display in general, and respective portions of the entire image data are displayed on the respective LED units. The LED units are provided with sets of RGB light emitting diodes aligned in a dot matrix on the substrate, and each unit operates in the same manner as the LED display described above. In the case of a large-scale LED display of a large size, one LED display is composed of, for example, a total of 120,000 LEDs in a 300 by 400 array.
On the other hand, it is customary to inspect a leakage current when the LED units are shipped. FIG. 4 shows how the leakage current is inspected with respect to LEDs 11 packaged in an LED panel 1A. According to a related art, in a case where the LED panel 1A having the packaging of a plurality of LEDs 11 is separated from a driving circuit substrate having thereon mounted driving circuits for driving the plurality of LEDs 11, as shown in FIG. 4, the inspection is conducted by using the LED panel 1A. As to the inspection of a reverse leakage current in an LED device, a constant voltage is applied in a reverse direction of the LEDs 11 (at the cathode side) and an ammeter is inserted at the anode side, under which conditions whether a leakage current is generated or not is measured by successively switching the respective lines. The shipping inspection is conducted by, for example, replacing an LED 11 generating a leakage current.
According to the above inspection method, however, there is a problem that the LED panel and the driving circuit substrate are separated and present independently, and the inspection is possible only at the time of production. According to this method, once the LED panel and the driving circuit substrate are electrically connected and combined with each other, the inspection is no longer possible. In other words, after the components are mounted, the horizontal driving units are connected to the LEDs at the cathode side, which makes it impossible to apply a reverse voltage. Also, in the case of a structure that the LED panel and the driving circuit substrate are formed in one body, a reverse voltage cannot be applied at the production inspection, and there is a problem that it is impossible to inspect an LED having a reverse leakage current being present therein.
The present invention is devised to solve the above problems, and therefore, is aimed at providing a driving circuit of a display apparatus and a display apparatus capable of detecting a light emitting element generating a leakage current in a reverse direction of the light emitting element even when the light emitting element is connected to the driving circuit.